The present invention relates generally to communication nodes and more particularly to Quality of Service (QoS) features in a single communication node for performing IP forwarding and ATM switching.
QoS covers a broad range of issues in computer networks. QoS features can take the form of preferred service for particular data flows. QoS features can also include congestion control. As used herein, the term xe2x80x9cQoS featuresxe2x80x9d refers to those features in a digital communication network that provide a capability to differentiate between data flows so that network service providers some traffic differently than other traffic. The need for QoS features arises from different types of network traffic having different transmission requirements. By way of example, to avoid echoes, voice traffic typically requires a 64 kbs bandwidth, with less than 100 ms of delay. Alternatively, non-interactive broadcast video typically requires a 271 Mbs bandwidth, but does not have a strict delay requirement. To be competitive, network service providers need to provide differentiated classes of service.
In conventional systems, ATM networks have been viewed as separate universes from IP networks. ATM networks work well for a subset of services, and IP networks work well for a different subset of services. Traditionally, ATM networks have been viewed as preferential for applications requiring more sophisticated QoS features. For example, the ATM Forum has defined five service categories for ATM: Constant Bit Rate (CBR); real-time Variable Bit Rate (rtVBR); non-real-time Variable Bit Rate (nrtVBR); Unspecified Bit Rate (UBR); and Available Bit Rate (ABR). When a service provider sets up an ATM virtual circuit (VC), the service provider and the user contract for one of the service categories. With each service category, comes a set of transmission priority parameters that are specific to the category.
However, as multimedia applications have infiltrated computer networking, IP QoS features have improved. Today, IP QoS features include the ReSerVation Protocol (RSVP); the Integrated Services models (IntServ); and the Integrated Services over Specific Link Layers (ISSLL). Together, these components provide comprehensive QoS features for end-to-end flows, but still do not provide all of the QoS features available from ATM. Additionally, this type of end-to-end flow regulation lacks the flexibility required for adapting to emerging technologies.
Given that neither IP nor ATM offer a complete multiservice solution, many service providers choose to operate dual networks. IP networks support applications such as Internet access and virtual private networks (VPNs), whereas ATM networks support Frame Relay (FR), VPNs, circuit emulation, private branch exchanges (PBX) and other applications where reliability and more rigorous QoS are a priority. These dual networks can be a complex and expensive aggregation of core routers connecting smaller Access Points of Presence (PoPs) to the core transport capacity. These structures are fragile, with frequent service outages due to performance limitations and equipment failures. Enterprises cannot afford to be exposed to significant down time due to failures or updates associated with conventional technology.
Accordingly, an object of the invention is to provide enhanced QoS features in a single communication node for performing IP forwarding and ATM switching.
A further object of the invention is to provide QoS features, which are capable of accommodating emerging technologies, in a single communication node.
Another object of the invention is to provide QoS features, which are capable of accommodating a variety of communication protocols, without requiring the maintenance of costly parallel networks.
These and other objects of the invention will be apparent with respect to the following description of the invention.
The invention is directed to a facility and related methods for providing Asynchronous Transfer Mode (ATM) and Internet Protocol (IP) Quality of Service (QoS) features in a digital communication node. Optionally, the QoS facility of the invention also provides Frame Relay (FR) QoS features. According to one embodiment of the invention, the facility comprises a plurality of logical input ports, a plurality of logical output ports, switching elements, routing elements and QoS elements.
The logical input ports are adapted for receiving input data flows from external data sources. Similarly, the logical output ports are adapted for transmitting output data flows to a plurality of external data destinations. According to the invention, the input and output data flows can be ATM-based data flows or IP-based data flows. The input and output data flows can also be IP over ATM. That is, IP packets can be carried in ATM cells. In a further embodiment of the invention, the logical input ports are included in a common physical interface. According to a further aspect, the input data flows through the common physical interface include Synchronous Optical Network (SONET) frames.
The switching elements are adapted for switching ATM data cells from one of the logical input ports toward at least one of the logical output ports, along a selected forwarding path. According to a further feature of the invention, the switching elements include ATM lookup elements for identifying toward which of the logical output ports particular ATM data cells should be switched.
The routing elements are adapted for routing IP data packets from one of the logical input ports toward at least one of the logical output ports along a selected forwarding path. According to a further embodiment of the invention, the routing elements include IP lookup elements for identifying toward which of the logical output ports to rout a particular IP data packet, in response to information contained in the particular IP data packet.
The QoS elements are common to the switching elements and the routing elements and provide ATM QoS features to the ATM data cells and IP QoS features to the to the IP data packets. Optionally, the ATM lookup elements are further adapted for determining which of the ATM QoS features should be applied to a particular ATM data cell. According to a time saving feature, the lookup elements identify a forwarding path and determine the applicable ATM QoS features in a single lookup operation.
The ATM QoS features include one or more of, Constant Bit Rate (CBR), Unspecified Bit Rate (UBR), non-real-time Variable Bit Rate (nrtVBR), real-time Variable Bit Rate (rtVBR) and Available Bit Rate (ABR), and the IP QoS features include one or more of, Provisional QoS, Differentiated Services, and Integrated Services.
In another embodiment of the invention, the facility for providing ATM and IP QoS features includes a mechanical housing that contains both the switching, routing and QoS elements. In this way, a facility according to one embodiment of the invention, provides an integrated system for switching ATM data cells, routing IP data packets and providing ATM and IP QoS features. Thus, a facility according to this embodiment of the invention enables service providers to avoid maintaining costly parallel networks; one for switching ATM data cells and one for routing IP data packets. The facility of the invention also enables service providers to provide different classes of service (e.g. coach, business and first class) for both ATM-based and IP-based data flows; thus, providing an additional source of revenue from clients willing to pay for enhanced bandwidth guarantees.
In alternative embodiments, the QoS facility provides call control elements. The call control elements enable the facility to form service contracts with client networks. The service contracts typically specify QoS features, such as bandwidth guarantees, that the communication node agrees to provide to data flows received from or transmitted to a client network. Optionally, the call control elements determine the available bandwidth of the communication node, and accept or deny requested service contracts in response to the available bandwidth.
Another embodiment of the invention provides traffic control elements. The traffic control elements interpret the bandwidth requirements associated with a service contract, and signal control information to devices along the forwarding path of the contracted data flow to reserve adequate bandwidth to provide the data flow with the contracted for QoS features.
A further feature of the invention is that the QoS elements are adapted to interpret the industry standard RSVP protocol. The RSVP protocol is a signaling protocol for an external data destination to request a service contract from the communication node. Typically, the service contract applies to data flows that the external data destination anticipates receiving from an external data source.
A facility according to one embodiment of the invention can be viewed as providing a plurality of logical functions along a data forwarding path. Classification, scheduling and policing are examples of such logical functions. Classification elements of the invention categorize received ATM data cells and IP data packets, based on which, if any, QoS features apply to the received cells and packets. The scheduling elements schedule routing of the IP data packets and switching of the ATM data cells in response to categorization by the classification elements. The policing elements monitor data flows to ensure that data flows received from external sources do not exceed agreed upon service contracts. According to one embodiment of the invention, the policing elements discard data that fails to conform to an agreed upon service contract. According to an alternative embodiment, the policing elements mark the nonconforming data. Data so marked is more likely to be discarded, should the communication node become congested.
According to another embodiment of the invention, the QoS facility employs alternative methods for identifying nonconforming data and for determining which data to discard if the communication node should become congested. By way of example, according to one feature, ATM data cells make up an ATM frame and the policing elements include Partial Packet Discard (PPD) elements for discarding selected additional ATM data cells included in an ATM frame, in response to having to discard one or more nonconforming ATM data cells included in the ATM frame. Typically, the PPD elements discard the ATM data cells of an ATM frame, which are received subsequent to the nonconforming ATM data cell, except for the last cell of the frame. The PPD elements do not discard the last cell of the ATM frame because that cell includes an end of a cell indicator.
An alternative approach to PPD is Early Packet Discard (EPD). According to a further aspect of the invention, the policing elements include EPD elements. According to the EPD protocol, the policing elements also include queuing elements for buffering the forwarding of ATM data cells, and the EPD elements discard entire ATM frames in response to the queuing elements reaching a selected level of fullness. By discarding the entire frame, the QoS facility avoids the overhead associated with transferring useless, partial ATM frames. It should be noted that PPD and EPD can be applied simultaneously by a policing element, and they can also be used at an output port for congestion control.
According to an alternative embodiment of the invention, the QoS facility comprises a plurality of logical input ports, a plurality of logical output ports, a plurality of communication modules, and QoS elements. The logical input ports are adapted for receiving input data flows from external data sources. The logical output ports are adapted for transmitting output data flows to a plurality of external data destinations. The data flows can be ATM-based data flows or IP-based data flows.
In a further aspect, the output ports include Random Early Detect (RED) elements. The RED elements monitor queue elements that buffer IP data packets and ATM data cells. In response to the queues reaching a selected average level of fullness, the RED elements substantially randomly discard IP data packets and ATM data cells. In this way, the QoS facility of the invention avoids the possibility of a data flow using up a disproportionate amount of bandwidth in the communication node.
The communication modules include IP packet routing elements for routing IP data packets from one of the logical input ports to one or more of the logical output ports. The communication modules also include ATM cell switching elements for switching ATM data cells form one of the logical input ports to one or more of the logical output ports.
The QoS elements provide ATM QoS features to ATM data cells, and provide IP QoS features to IP data packets. The ATM QoS features include one or more of, Constant Bit Rate (CBR), Unspecified Bit Rate (UBR), non-real-time Variable Bit Rate (nrtVBR), real-time Variable Bit Rate (rtVBR) and Available Bit Rate (ABR). The IP QoS features include one or more of, Provisional QoS, Differentiated Services, and Integrated Services. In a further embodiment, at least some of the QoS elements are distributed among the communication modules.
According to a further feature, the QoS facility includes an interconnect. The interconnect is in digital communication with the communication modules and is adapted for forwarding ATM data cells and IP data packets between the communication modules. In one preferred embodiment, the interconnect is in electrical communication with the communication modules, while in other embodiments the interconnect is coupled to the communication modules via fiber optical connections. Optionally, at least some of the QoS elements are included in the interconnect.
The QoS elements can also include a control processor for controlling operation of the QoS elements. In a further aspect, the control processor populates tables that are at least in part representative of the QoS features to be applied to received ATM data cells and received IP data packets. Optionally, the QoS elements include lookup elements that access the tables and schedule routing of IP data packets and switching of ATM data cells through the communication node, based at least in part on the populated tables. In a further embodiment, each of the communication modules include a communication module processor. The communication module processors are in communication with the control processor and assist the control processor in controlling the QoS elements.
According to a further embodiment of the invention, the communication modules include a queuing structure for intermediately storing ATM data cells and IP data packets transferred from the interconnect to the communication modules for output via one or more of the logical output ports. According to another aspect, the communication modules include one or more logical output ports associated with each of the physical output ports. Additionally, the queuing structure further comprises a plurality of output queues associated with each of the physical output ports, wherein each plurality of output queues is adapted for intermediately storing IP data packets and ATM data cells destined for output through an associated physical output port. According to another feature, each of the queues included in a particular plurality of queues has an assigned priority relative to other queues included in the plurality. Data stored in queues having a relatively higher priority is scheduled for output in preference to data stored in relatively lower priority queues. Which, if any, of the ATM and IP QoS features are associated with the data determines in which queue the data is stored. It also determines the output scheduling of the data stored in the queue. According to another feature, congestion control elements are used to monitor the amount of data in the queues and selectively drop or mark IP packets and ATM cells when the queue occupations reach selected thresholds.
In a further feature of the invention, the queuing structure includes a traffic shaping element comprised of a calendar queue. The calendar queue intermediately stores at least selected ATM data cells and IP data packets destined for the output queues. The traffic shaping element schedules the transfer of ATM data cells and IP data packets from the calendar queue to the output queues, based at least in part, on which of the ATM and IP QoS features apply to the ATM data cells and IP data packets stored in the calendar queue.
According to a further practice of the invention, the queuing structure also includes an output stack. The output stack is adapted for intermediately storing ATM data cells and IP data packets that are destined for transfer from one of the output queues.
In an alternative embodiment, the invention comprises a method for providing ATM and IP QoS features in a digital communication node. The method comprises the steps of: receiving ATM data cells and IP data packets into the digital communication node; determining if any ATM QoS features are associated with a received ATM cell, and if so, assigning a priority for forwarding the received ATM data cell through the digital communication node, wherein the priority is representative of the ATM QoS features associated with the cell; determining if any IP QoS features are associated with a received IP data packet, and if so, assigning a priority for forwarding the received IP packet through the digital communication node, wherein the priority is representative of the IP QoS features associated with the packet; scheduling forwarding of received ATM cells and received IP packets through the communication node, based at least in part on the assigned priority; forwarding the received ATM cells and IP packets to an external destination.
In further embodiments, the invention includes additional elements and methods for providing ATM and IP QoS features in a digital communication node.